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Now, if our reality really is entirely physical, and everything really is just the result of natural processes, then needless to say it doesn’t just have some serious implications for God’s existence; it has implications for other major metaphysical questions too. For instance, does a purely naturalistic worldview leave any room for the human soul? Is everything about our minds and our personalities also just the result of purely physical processes? Or is it possible for someone’s personality to exist independent of their physical existence?

As it turns out, this is another question where science has already given us some clear answers. As Steve Ramirez writes:

If neuroscience has taught us anything in the last two decades, it’s that the separation between “mental” and “physical” phenomena simply does not exist. We know this because of the tragic loss-of-function experiments that affect millions of people each year. Broken brain pieces give rise to broken thoughts. Pharmaceutical treatments, however, help glue together these broken thoughts. No amount of philosophy will fight off depression, but a blue pill called fluoxetine is effective. Schizophrenic symptoms shatter lives, but risperidone can intervene and help turn lives around. Minds can go into fits of mania, but these can be curbed by lithium. Parkinsonian symptoms are debilitating beyond belief, but they can be temporally kept at bay thanks to L-Dopa. Alzheimer’s has all sorts of dramatic effects on memory; donepezil can at least partly treat this kind of dementia. The general principle underlying the effectiveness of these pills is simple: physical stuff interacts only with physical stuff, and the mind is just that. Like a pill, it has a measurable mechanism of action.

Adam Benforado elaborates:

The soft tissue of the brain is the starting point for everything we do.

What is allowing you to perceive the words of this sentence, understand their meaning, remember the contents of the previous section, feel the pages or device you hold in your hands, and decide to continue on to the next paragraph?

The answer is nothing more than neurons, synapses, and neurotransmitters. Take away these electrochemical interactions and that’s it: no thoughts, no emotions, no choices, no behavior.

Even for those with no religious inclination, it doesn’t feel that way. It feels as if we have something like a “soul” – independent, purposeful, and rational – directing our actions. How could that thing be nothing more than neurons generating electrical impulses, triggering chemical signals carried to other neurons? It seems improbable, impossible even. But that is the truth.

[…]

Even back in [the 1800s], there was some appreciation of the fact that particular areas of the brain might be involved in regulating particular behaviors. Perhaps the most famous example was that of a twenty-five-year-old supervisor for the Rutland and Burlington Railroad in Vermont, Phineas P. Gage.

Gage’s fame all came down to a tragic and miraculous event one day in 1848, when he decided to pack explosive powder into a rock using a metal rod. His actions (perhaps not unexpectedly, to our cautious modern eyes) triggered a sudden explosion, and the thirteen-pound piece of iron was driven up through his left cheek and straight out of the top of his head.

In an amazing bit of luck, despite horrible damage to his prefrontal cortex and other areas of his brain, Gage survived with most of his physical and intellectual capacities preserved. But as his friends quickly noticed, Gage was “no longer Gage.” Respectful, pleasant, and dutiful before the accident, Gage became lazy, boorish, and foul-tempered. The injury to particular parts of his brain seemed to change particular aspects of his behavior.

[…]

Perhaps a more relevant case […] is one reported in the Archives of Neurology more than 150 years after Gage suffered his injury.

[…]

In 2000, a married forty-year-old Virginia schoolteacher, Mr. Oft, who had never had abnormal sexual urges, suddenly began collecting child pornography and, soon thereafter, attempted to molest his prepubescent stepdaughter. As a first-time offender, the man was diverted to a twelve-step inpatient program for treatment of his sexual addiction. Any serious slip-up and he would be sent to prison. Even though he understood that risk, did not want to be incarcerated, and seemed to know that what he was doing was wrong, he began to solicit sex from the staff at the rehabilitation facility.

Oft was kicked out of the program, of course, and was set to be sentenced the next day, when he developed an intense headache. It was so bad that he had to go to the hospital. But no sooner had his neurological examination begun than he was propositioning the women in the room and openly discussing his fear that he would rape his landlady.

With his bad behavior in clear evidence, the doctors might have written off the headache as a mere ruse to delay going to prison, but instead they ordered a brain scan. What they found was staggering: a tumor, as big as an egg, in the right orbitofrontal area.

The surgery to remove it provided similarly stunning results: with the tumor excised, Oft lost all interest in pornography and easily completed the Sexaholics Anonymous program that had previously been such a struggle. Seven months later, he was permitted to return home.

Oft’s apparent recovery, however, did not last. By October 2001, his headache had reappeared – as had his secret collection of explicit materials. Were the two again connected? Sure enough, when doctors ordered another brain scan, they found that the tumor had grown back. And with a second surgery, in February 2002, the sexual deviance vanished once again.

Cases like these provide vivid illustrations of how deficits in the brain can produce profound changes in behavior.

[…]

[And] the evidence related to traumatic brain injuries is similarly stark: while less than 9 percent of those outside of prison have experienced such trauma, roughly 60 percent of those in prison have had at least one such injury.

Pinker delves even deeper into this research, mentioning Gage’s story along with some other equally remarkable examples:

One can say that the information-processing activity of the brain causes the mind, or one can say that it is the mind, but in either case the evidence is overwhelming that every aspect of our mental lives depends entirely on physiological events in the tissues of the brain.

When a surgeon sends an electrical current into the brain, the person can have a vivid, lifelike experience. When chemicals seep into the brain, they can alter the person’s perception, mood, personality, and reasoning. When a patch of brain tissue dies, a part of the mind can disappear: a neurological patient may lose the ability to name tools, recognize faces, anticipate the outcome of his behavior, empathize with others, or keep in mind a region of space or of his own body. (Descartes was thus wrong when he said that “the mind is entirely indivisible” and concluded that it must be completely different from the body.) Every emotion and thought gives off physical signals, and the new technologies for detecting them are so accurate that they can literally read a person’s mind and tell a cognitive neuroscientist whether the person is imagining a face or a place. Neuroscientists can knock a gene out of a mouse (a gene also found in humans) and prevent the mouse from learning, or insert extra copies and make the mouse learn faster. Under the microscope, brain tissue shows a staggering complexity – a hundred billion neurons connected by a hundred trillion synapses – that is commensurate with the staggering complexity of human thought and experience. Neural network modelers have begun to show how the building blocks of mental computation, such as storing and retrieving a pattern, can be implemented in neural circuitry. And when the brain dies, the person goes out of existence. Despite concerted efforts by Alfred Russel Wallace and other Victorian scientists, it is apparently not possible to communicate with the dead.

Educated people, of course, know that perception, cognition, language, and emotion are rooted in the brain. But it is still tempting to think of the brain as it was shown in old educational cartoons, as a control panel with gauges and levers operated by a user – the self, the soul, the ghost, the person, the “me.” But cognitive neuroscience is showing that the self, too, is just another network of brain systems.

The first hint came from Phineas Gage, the nineteenth-century railroad worker familiar to generations of psychology students. Gage was using a yard-long spike to tamp explosive powder into a hole in a rock when a spark ignited the powder and sent the spike into his cheekbone, through his brain, and out the top of his skull. Phineas survived with his perception, memory, language, and motor functions intact. But in the famous understatement of a co-worker, “Gage was no longer Gage.” A piece of iron had literally turned him into a different person, from courteous, responsible, and ambitious to rude, unreliable, and shiftless. It did this by impaling his ventromedial prefrontal cortex, the region of the brain above the eyes now known to be involved in reasoning about other people. Together with other areas of the prefrontal lobes and the limbic system (the seat of the emotions), it anticipates the consequences of one’s actions and selects behavior consonant with one’s goals.

Cognitive neuroscientists have not only exorcised the ghost but have shown that the brain does not even have a part that does exactly what the ghost is supposed to do: review all the facts and make a decision for the rest of the brain to carry out. Each of us feels that there is a single “I” in control. But that is an illusion that the brain works hard to produce, like the impression that our visual fields are rich in detail from edge to edge. (In fact, we are blind to detail outside the fixation point. We quickly move our eyes to whatever looks interesting, and that fools us into thinking that the detail was there all along.) The brain does have supervisory systems in the prefrontal lobes and anterior cingulate cortex, which can push the buttons of behavior and override habits and urges. But those systems are gadgets with specific quirks and limitations; they are not implementations of the rational free agent traditionally identified with the soul or the self.

One of the most dramatic demonstrations of the illusion of the unified self comes from the neuroscientists Michael Gazzaniga and Roger Sperry, who showed that when surgeons cut the corpus callosum joining the cerebral hemispheres, they literally cut the self in two, and each hemisphere can exercise free will without the other one’s advice or consent. Even more disconcertingly, the left hemisphere constantly weaves a coherent but false account of the behavior chosen without its knowledge by the right. For example, if an experimenter flashes the command “WALK” to the right hemisphere (by keeping it in the part of the visual field that only the right hemisphere can see), the person will comply with the request and begin to walk out of the room. But when the person (specifically, the person’s left hemisphere) is asked why he just got up, he will say, in all sincerity, “To get a Coke” – rather than “I don’t really know” or “The urge just came over me” or “You’ve been testing me for years since I had the surgery, and sometimes you get me to do things but I don’t know exactly what you asked me to do.” Similarly, if the patient’s left hemisphere is shown a chicken and his right hemisphere is shown a snowfall, and both hemispheres have to select a picture that goes with what they see (each using a different hand), the left hemisphere picks a claw (correctly) and the right picks a shovel (also correctly). But when the left hemisphere is asked why the whole person made those choices, it blithely says, “Oh, that’s simple. The chicken claw goes with the chicken, and you need a shovel to clean out the chicken shed.”

The spooky part is that we have no reason to think that the baloney-generator in the patient’s left hemisphere is behaving any differently from ours as we make sense of the inclinations emanating from the rest of our brains. The conscious mind – the self or soul – is a spin doctor, not the commander in chief. Sigmund Freud immodestly wrote that “humanity has in the course of time had to endure from the hands of science three great outrages upon its naïve self-love”: the discovery that our world is not the center of the celestial spheres but rather a speck in a vast universe, the discovery that we were not specially created but instead descended from animals, and the discovery that often our conscious minds do not control how we act but merely tell us a story about our actions. He was right about the cumulative impact, but it was cognitive neuroscience rather than psychoanalysis that conclusively delivered the third blow.

Cognitive neuroscience is undermining not just the Ghost in the Machine but also the Noble Savage. Damage to the frontal lobes does not only dull the person or subtract from his behavioral repertoire but can unleash aggressive attacks. That happens because the damaged lobes no longer serve as inhibitory brakes on parts of the limbic system, particularly a circuit that links the amygdala to the hypothalamus via a pathway called the stria terminalis. Connections between the frontal lobe in each hemisphere and the limbic system provide a lever by which a person’s knowledge and goals can override other mechanisms, and among those mechanisms appears to be one designed to generate behavior that harms other people.

Nor is the physical structure of the brain a blank slate. In the mid-nineteenth century the neurologist Paul Broca discovered that the folds and wrinkles of the cerebral cortex do not squiggle randomly like fingerprints but have a recognizable geometry. Indeed, the arrangement is so consistent from brain to brain that each fold and wrinkle can be given a name. Since that time neuroscientists have discovered that the gross anatomy of the brain – the sizes, shapes, and connectivity of its lobes and nuclei, and the basic plan of the cerebral cortex – is largely shaped by the genes in normal prenatal development. So is the quantity of gray matter in the different regions of the brains of different people, including the regions that underlie language and reasoning.

This innate geometry and cabling can have real consequences for thinking, feeling, and behavior. […] Babies who suffer damage to particular areas of the brain often grow up with permanent deficits in particular mental faculties. And people born with variations on the typical plan have variations in the way their minds work. According to a recent study of the brains of identical and fraternal twins, differences in the amount of gray matter in the frontal lobes are not only genetically influenced but are significantly correlated with differences in intelligence. A study of Albert Einstein’s brain revealed that he had large, unusually shaped inferior parietal lobules, which participate in spatial reasoning and intuitions about number. Gay men are likely to have a smaller third interstitial nucleus in the anterior hypothalamus, a nucleus known to have a role in sex differences. And convicted murderers and other violent, antisocial people are likely to have a smaller and less active prefrontal cortex, the part of the brain that governs decision making and inhibits impulses. These gross features of the brain are almost certainly not sculpted by information coming in from the senses, which implies that differences in intelligence, scientific genius, sexual orientation, and impulsive violence are not entirely learned.

The research on those patients whose left and right brain hemispheres have been surgically separated (AKA “split-brain” patients) is especially fascinating. As V. S. Ramachandran points out, it creates some glaring problems for the idea of the soul:

And there are still other considerations here too – like the fact that general anesthesia (a physical treatment applied to your physical brain) makes your consciousness go away entirely while it’s in your system. This is yet another strong piece of evidence that consciousness doesn’t come from an immaterial soul; if consciousness was completely independent of your physical body, then why would anesthetizing your physical brain have any effect on it?

But all these questions ultimately circle back around to the big one mentioned earlier, which we already discussed with regard to (the supposedly immaterial) God. If you believe that a person’s physical body is controlled by an immaterial soul, the biggest question you have to answer is simply how such a physical/non-physical interaction could even theoretically work in the first place. After all, like I said before, there would have to be some kind of interaction there; if the non-physical didn’t interact with the physical in any way, there’d be no way for it to have any effect on it. But by what mechanism, exactly, would it be possible for something non-physical to interact with something physical (unless the non-physical substance was somehow manifesting itself as a physical force, which would be detectable)? And for that matter, what would it even mean to say that a non-physical substance could exist at all? Isn’t “non-physical substance” an oxymoron? Here’s QualiaSoup:

In the philosophy of mind, substance dualism is the view that there are two kinds of substance: physical (or material) substance, and the non-physical (or immaterial) substance of souls, minds, or consciousness.

[…]

Something that instantly triggers our scepticism of this philosophy is the use of the term “non-physical substance.” What exactly is this supposed to mean? Let’s be clear: concepts like truth and justice may be defined as abstract ideas. In that sense, it’s reasonable to call them non-physical concepts. But they don’t have their own independently active existence. What dualists are proposing is a non-physical thing existing in addition to brains and physical matter, as an active, thinking entity.

[…]

How is a thing with no conceivable physical aspect meant to think? Or do anything at all? In what sense could it even be said to exist? If minds are entirely non-physical, what anchors them to particular bodies? These are not questions to be swept aside, nor do they reflect some irrational dread of dualism and its implications. They reflect a reasonable expectation that dualists who make the factual claim that mind or consciousness is a non-physical substance should make their claim comprehensible. Dualists who can’t or won’t explain coherently what they’re proposing have no genuine complaint if dualism gets a poor reception. Likening a non-physical substance to energy, magnetic fields, or sound waves channeled by a radio set is obviously a non-starter, as those things are all physical. Saying a non-physical thing is like a physical thing (except it’s not physical) glosses over the very thing that needs explaining.

Again, the central point here is that physical stuff can only interact with anything else physically. However you want to define the human mind (or personality, or “soul”), the one thing that science keeps showing us again and again is that it can only be the result of purely physical processes – just like everything else in the universe. If our brains and bodies were being controlled by immaterial souls, we’d constantly be seeing them do things without any detectable physical causes, as if they were possessed by poltergeists or something. But all we ever see is that physical actions are driven by physical causes, top to bottom.

Now, naturally this has implications beyond just whether the soul exists; it also extends to concepts like free will that are similarly central to so many religious doctrines. After all, if everything that we think and do is just a product of how the physical components of our brains operate, and if the way our brains operate is determined solely by the interactions of the atoms that make them up, and if the way those atoms interact is dictated solely by the unchangeable and unbreakable laws of physics and chemistry (just as surely as are the paths of colliding billiard balls), then once you get down to the most basic level, we’re really nothing but biological machines – albeit extremely complex ones – and we can’t be said to possess true free will any more than any other mechanical object (like, say, a pocket watch) can. It might feel from the inside like we have total freedom over our thoughts and actions – and for practical purposes, it might be useful for us to act as if we do – but this feeling is an illusion. The true causes of our thoughts and actions are all the electro-chemical processes happening “under the hood” of our brains – and the only reason why it seems otherwise is because we aren’t consciously aware of these processes as they’re happening. Here’s David Eagleman:

As far as we can tell, all activity in the brain is driven by other activity in the brain, in a vastly complex, interconnected network. For better or worse, this seems to leave no room for anything other than neural activity – that is, no room for a ghost in the machine. To consider this from the other direction, if free will is to have any effect on the actions of the body, it needs to influence the ongoing brain activity. And to do that, it needs to be physically connected to at least some of the neurons. But we don’t find any spot in the brain that is not itself driven by other parts of the network. Instead, every part of the brain is densely interconnected with – and driven by – other brain parts. And that suggests that no part is independent and therefore “free.”

So in our current understanding of science, we can’t find the physical gap in which to slip free will – the uncaused causer – because there seems to be no part of the machinery that does not follow in a causal relationship from the other parts. Everything stated here is predicated on what we know at this moment in history, which will certainly look crude a millennium from now; however, at this point, no one can see a clear way around the problem of a nonphysical entity (free will) interacting with a physical entity (the stuff of the brain).

But let’s say that you still intuit very strongly that you have free will, despite the biological concerns. Is there any way neuroscience can try to directly test for free will?

In the 1960s, a scientist named Benjamin Libet placed electrodes on the heads of subjects and asked them to do a very simple task: lift their finger at a time of their own choosing. They watched a high-resolution timer and were asked to note the exact moment at which they “felt the urge” to make the move.

Libet discovered that people became aware of an urge to move about a quarter of a second before they actually made the move. But that wasn’t the surprising part. He examined their EEG recordings – the brain waves – and found something more surprising: the activity in their brains began to rise before they felt the urge to move. And not just by a little bit. By over a second. […] In other words, parts of the brain were making decisions well before the person consciously experienced the urge. […] It seems that our brains crank away behind the scenes – developing neural coalitions, planning actions, voting on plans – before we receive the news that we’ve just had the great idea to lift a finger.

Libet’s experiments caused a commotion. Could it be true that the conscious mind is the last one in the chain of command to receive any information? Did his experiment drive the nail into the coffin of free will? Libet himself fretted over this possibility raised by his own experiments, and finally suggested that we might retain freedom in the form of veto power. In other words, while we can’t control the fact that we get the urge to move our finger, perhaps we retain a tiny window of time to stop the lifting of our finger. Does this save free will? It’s difficult to say. Despite the impression that a veto might be freely chosen, there is no evidence to suggest that it, too, wouldn’t be the result of neural activity that builds up behind the scenes, hidden from conscious view.

People have proposed several other arguments to try to save the concept of free will. For example, while classical physics describes a universe that is strictly deterministic (each thing follows from the last in a predictable way), the quantum physics of the atomic scale introduces unpredictability and uncertainty as an inherent part of the cosmos. The fathers of quantum physics wondered whether this new science might save free will. Unfortunately, it doesn’t. A system that is probabilistic and unpredictable is every bit as unsatisfying as a system that is deterministic, because in both cases there’s no choice. It’s either coin flips or billiard balls, but neither case equates to freedom in the sense that we’d desire to have it.

Other thinkers trying to save free will have looked to chaos theory, pointing out that the brain is so vastly complex that there is no way, in practice, to determine its next moves. While this is certainly true, it doesn’t meaningfully address the free-will problem, because the systems studied in chaos theory are still deterministic: one step leads inevitably to the next. It is very difficult to predict where chaotic systems are going, but each state of the system is causally related to the previous state. It is important to stress the difference between a system being unpredictable and it being free. In the collapse of a pyramid of ping-pong balls, the complexity of the system makes it impossible to predict the trajectories and final positions of the balls – but each ball nonetheless follows the deterministic rules of motion. Just because we can’t say where it’s all going does not mean that the collection of balls is “free.”

So despite all our hopes and intuitions about free will, there is currently no argument that convincingly nails down its existence.

And Harris (whose short book Free Will is a great read if you’re intrigued and/or unnerved by this whole discussion) adds:

Free will is actually more than an illusion (or less) in that it cannot even be rendered coherent conceptually, since no one has ever described a manner in which mental and physical events could arise that would attest to its existence. Surely, most illusions are made of sterner stuff than this. If, for instance, a man believes that his dental fillings are receiving radio broadcasts, or that his sister has been replaced by an alien who looks exactly like her, we would have no difficulty specifying what would have to be true of the world for his beliefs to be, likewise, true. Strangely, our notion of “free of will” achieves no such intelligibility. As a concept, it simply has no descriptive, or even logical, moorings. Like some perverse, malodorous rose, however we might attempt to enjoy its beauty up close, it offers up its own contradiction.

The idea of free will is an ancient artifact of philosophy, of course, as well as a subject of occasional, if guilty, interest among scientists. […] It has long been obvious, however, that any description of the will in terms of causes and effects sets us sliding toward a moral and logical crevasse, for either our wills are determined by prior causes, and we are not responsible for them, or they are the product of chance, and we are not responsible for them. The notion of free will seems particularly suspect once we begin thinking about the brain. If a man’s “choice” to shoot the president is determined by a certain pattern of neural activity, and this neural activity is in turn the product of prior causes – perhaps an unfortunate coincidence of an unhappy childhood, bad genes, and cosmic-ray bombardment – what can it possibly mean to say that his will is “free”? Despite the clever exertions of many philosophers who have sought to render free will “compatible” with both deterministic and indeterministic accounts of mind and brain, the project appears to be hopeless. The endurance of free will, as a problem in need of analysis, is attributable to the fact that most of us feel that we freely author our own actions and acts of attention (however difficult it may be to make sense of this notion in logical or scientific terms). It is safe to say that no one was ever moved to entertain the existence of free will because it holds great promise as an abstract idea.

In physical terms, every action is clearly reducible to a totality of impersonal events merely propagating their influence: genes are transcribed, neurotransmitters bind to their receptors, muscle fibers contract, and John Doe pulls the trigger on his gun. For our commonsense notions of agency to hold, our actions cannot be merely lawful products of our biology, our conditioning, or anything else that might lead others to predict them – and yet, were our actions to be actually divorced from such a causal network, they would be precisely those for which we could claim no responsibility. It has been fashionable, for several decades now, to speculate about the manner in which the indeterminacy of quantum processes, at the level of the neuron or its constituents, could yield a form of mental life that might stand free of the causal order; but such speculation is entirely oblique to the matter at hand – for an indeterminate world, governed by chance or quantum probabilities, would grant no more autonomy to human agents than would the incessant drawing of lots. In the face of any real independence from prior causes, every gesture would seem to merit the statement “I don’t know what came over me.” Upon the horns of this dilemma, fanciers of free will can often be heard making shrewd use of philosophical language, in an attempt to render our intuitions about a person’s moral responsibility immune to worries about causation. […] Although we can find no room for it in the causal order, the notion of free will is still accorded a remarkable deference in philosophical and scientific literature, even by scientists who believe that the mind is entirely dependent upon the workings of the brain.

What most people overlook is that free will does not even correspond to any subjective fact about us. Consequently, even rigorous introspection soon grows as hostile to the idea of free will as the equations of physics have, because apparent acts of volition merely arise, spontaneously (whether caused, uncaused, or probabilistically inclined, it makes no difference), and cannot be traced to a point of origin in the stream of consciousness. A moment or two of serious self-scrutiny and the reader might observe that he no more authors the next thought he thinks than the next thought I write.

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